Office machines for processing text data to produce hard copies utilize display screens for presenting to an operator visual text as it would appear on hard copy. Typically, such machines incorporate a conventional typewriter keyboard with additional control keys for operator interface with the system controls. The operator keystrokes are displayed on a screen quite similar to a home television receiver screen. This screen either displays a full page of text, a partial page, or in some machines only a single line of text. The display not only provides a visual presentation to the operator of the text being prepared but also provides prompting instructions for the operator of how to interface with the machine.
Responding to the keyboard strokes of an operator are system controls including programmed computers which prepare the text display. Most present day text processing systems include electronics hardware programmed to evaluate the operator keystrokes and to control the display. This electronics hardware includes memory for storing character data and instruction data for future use in editing and the preparation of hard copy. Ease of operation of the machine for the operator is in large part determined by the electronics and the associated computers and programs therefor.
One area of importance in determining the acceptability of a text processing system is the ability to display to the operator and prepare hard copy of characters in a mixed pitch format. The pitch of a character is defined as the horizontal space on a line reserved for a character. Heretofore, some office machines have provided variable pitch, that is, each character and symbol has a defined space depending upon the character or symbol. However, most office machines have a fixed pitch with the most common being the 10-pitch and 12-pitch format. A 10-pitch format has ten characters per inch of horizontal line space and a 12-pitch format has twelve characters per inch of line space. Many documents, however, are formatted with a combination of mixed character pitch formats, such as a combination of 10 character pitch and 12 character pitch. The character pitch will usually not change between characters on a line but mixed pitch will appear in lines or paragraphs on a page. For example, a columnar presentation of data may be formatted in 12-pitch while text may be formatted in 10-pitch.